Airway Pressure Interpretation — FRCA Final MCQ

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ModerateIntensive Care MedicineAirway Pressure InterpretationFRCA Final

A deeply sedated ICU patient is passively ventilated using constant-flow volume-controlled ventilation. With tidal volume, inspiratory flow and PEEP unchanged, peak airway pressure acutely rises from 25 to 42 cmH2O. Plateau pressure measured during an end-inspiratory hold remains 20 cmH2O. Which is the most likely cause?

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Correct answer: E — Increased airway resistance from bronchospasm or tracheal-tube secretions

The correct answer is E. During passive constant-flow volume-controlled ventilation, peak airway pressure equals PEEP plus elastic and resistive pressures. Plateau pressure is measured at zero flow and therefore reflects PEEP plus the elastic pressure of the respiratory system. Here, the peak-to-plateau gradient rises from 5 to 22 cmH2O while plateau pressure remains unchanged, demonstrating an acute increase in airflow resistance. Bronchospasm, secretions within the tracheal tube, tube kinking or circuit obstruction produce this pattern. Pneumothorax, worsening ARDS, pulmonary oedema and abdominal compartment syndrome primarily reduce respiratory-system compliance; with unchanged tidal volume, they would be expected to increase plateau pressure as well as peak pressure.

Reference: Szafran JC, Patel BK. Invasive Mechanical Ventilation—Figures 1 and 2: inspiratory-hold measurements and interpretation of changing lung mechanics. Critical Care Clinics. 2024;40(2):255-273. https://pubmed.ncbi.nlm.nih.gov/38432695/